Riboflavin, also known as vitamin B.sub.2, vitamin G and lactoflavin, has physiological significance in the metabolism of protein, fat, and nucleic acids. Because it is considered to be an essential B vitamin, riboflavin is added to poultry and livestock feeds as well as human foodstuffs to supplement naturally occurring levels.
Riboflavin has typically been produced by chemical synthesis or by fermentation. Chemical synthesis can result in a riboflavin product contaminated with reactant or byproduct chemicals. Purification of riboflavin by removal of said contaminants can be expensive. Moreover, the synthetic process can result in the generation of toxic or hazardous wastes that must be properly disposed.
For these reasons, a "natural" riboflavin product can be preferred by manufacturers of human and animal food products. Because "natural" riboflavin is produced by the fermentation process, its impurities are largely cellular structures and moieties. Such impurities do not present the toxicity hazards or disposal problems that chemical reactant or byproduct contaminants can present.
However, riboflavin produced by recovery from fermentation broth has typically had an inferior level of purity compared to riboflavin produced by chemical synthesis.
A method for recovery of riboflavin from fermentation broth is described in U.S. Pat. No. 2,822,361 to Morehouse (1958). The Morehouse method involves the following steps: (1) heating of a fermentation broth having a pH of 4.5-5.0 to lyse the cells and dissolve the riboflavin; (2) filtering to separate cells from solubilized riboflavin; (3) precipitating the riboflavin in a reduced form by the treatment of the filtrate with a reducing agent; (4) adjusting the pH to at least 9.5 to solubilize the reduced riboflavin precipitate; (5) oxidizing the reduced riboflavin in the high pH solution; (6) precipitating the oxidized riboflavin from the high pH solution by adjustment of the pH to 4.0-7.5; and (7) separating the riboflavin precipitate from its mother liquor. The starting material for the Morehouse method is a fermentation broth containing about 1 g/l riboflavin. The purity of the final product is reported to be 87%.
Other patents involving riboflavin recovery or conversion of riboflavin from one crystal type to another appear to be cumulative of steps found in the Morehouse process. The precipitation of the "riboflavin precurser" and its subsequent oxidation in the method of U.S. Pat. No. 2,815,341 to Dale (1957) appears to be cumulative of the Morehouse steps of precipitation of the riboflavin in reduced form followed by oxidation. Additionally, the solubilization of riboflavin by adjustment of the pH to alkali conditions and the subsequent step of riboflavin crystallization by reducing the pH by acidification in U.S. Pat. No. 2,797,215 to Dale (1957) appears to be cumulative to the Morehouse steps of solubilization of riboflavin followed by crystallization.
The Morehouse method has the drawback that it cannot recover the majority of riboflavin from concentrated (i.e., more than 1 g/l) riboflavin starting solutions due to its method for solubilization of riboflavin, i.e., by heating the broth. Separation of riboflavin from the cells in the broth is accomplished by hot filtration. Because only relatively small amounts of riboflavin can be solubilized by heating, the Morehouse method is not suitable for starting solutions containing riboflavin in concentrations greater than about 1 g/l.
Consequently, there is a need for a method for recovery of riboflavin from fermentation broths and other materials having a riboflavin concentration greater than 1 g/l. Moreover, a method should preferably produce a final riboflavin product having a purity comparable to that of riboflavin produced by chemical synthesis. The method should be relatively simple so as to reduce the costs inherent in lengthy and complex procedures such as Morehouse
It has been found that the present invention can satisfy the above requirements. The instant process has additional advantages over known recovery procedures. The subject method contains only one riboflavin precipitation step and therefore shortens process time and lessens expense compared to the Morehouse process. Further, the precipitation of oxidized or non-reduced riboflavin in the instant process can be accomplished directly from a fermentation broth rather than from a purified riboflavin solution as provided by Morehouse and Dale (U.S. Pat. No. 2,797,215). The present method also produces a product having a purity comparable to the purity of chemically synthesized riboflavin.